The invention relates to a method for operating a non-railborne hybrid vehicle having means for changing an operating state of its internal combustion engine.
The solution shown in the publication document EP 0 556 942 relates to a non-railborne series hybrid vehicle with a combustion engine, a generator coupled to its crankshaft, power electronics, an electronic control as well as at least one electric drive motor.
Since the vehicle user generally expects an acceleration of the vehicle when he presses the gas pedal more heavily, there is required an undelayed, monotonic increase in the driving torque without the occurrence of tractive force, and a corresponding monotonic increase of the generator torque (column 5, lines 33 to 41).
Given this condition, the driving and generator power likewise increase monotonically due to the physical relationship power equals torque multiplied by the rotational speed (column 5, lines 8 to 15 as well as 42 to 49).
In EP 0 556 942 then, for the mentioned case of a pending increase in power of the combustion engine, it is suggested at first not to increase to torque absorbed by the generator to the degree which is the case with the torque produced internally in the combustion engine (column 5, lines 15 to 21).
The excess power of the combustion engine arising from this has the effect that its rotational speed may increase more swiftly and that the nominal power is available as soon as possible (column 5, lines 22 to 29).
The disadvantage of this solution however lies in the fact that a quicker increase in rotational speed of the combustion engine is by matter of course achieved at the cost of vehicle acceleration. Both criteria "a quick increase in rotational speed" as well as "an immediate increase in the driving power" restrict one another.
In an extreme case, although a swift increase in rotational speed and thus a quick attainment of the aimed power of the combustion engine is made possible, during this acceleration interval however, there is at the most only a slight acceleration of the vehicle possible. The desired acceleration of the vehicle occurs delayed only on reaching the nominal rotational speed.
Reversely, a direct acceleration of the vehicle has the result that the rotational speed of the combustion engine increases only slowly and the final driving power sought after is only gradually achieved. Due to the fact that the generator in this case heavily loads the combustion engine, narrow limits are set for the choice of optimal operating points in the torque-speed characteristic curve. For example, in this manner, during the acceleration phase, a minimal fuel consumption can hardly be achieved.
In the case of a foreseen reduction in power of the combustion engine, the torque absorbed by the generator, in contrast to the previously described case, is always kept greater that the torque produced by the combustion engine. Analogously, here the generator power reduces monotonically until the new operating point of the combustion engine has been reached (column 5, line 50 to 58, and column 6 lines 1 to 6). It is however not mentioned as to what happens with the excess generator power during such a change in operating point.